National Geographic : 2017 Sep
Meth displaces dopamine into synapse Cocaine blocks dopamine removal from synapse Heroin blocks dopamine inhibitors In VTA In brain reward system Dopamine floods synapse Dopamine transporters remove excess dopamine from synapse Dopamine temporarily floods synapse Dopamine receptors Dopamine inhibitor receptors Synapse Dopamine Dopamine stored in neurons Dopamine transporters Terminal of neuron Dendrite DOPAMINE Ventral tegmental area (VTA) Dopamine is produced here and flows outward along neurons distributed throughout the brain’s reward system. Dorsal striatum Neurons here help form habits by identifying enjoyable patterns, such as the anticipation of buying drugs. Nucleus accumbens A hot spot within this key part of the craving circuitry amplifies the response to pleasure. Orbitofrontal cortex This hot spot gives a sense of gratification but is also the first to shut down if a person has indulged too much. Prefrontal cortex The amino acid glutamate, produced here, interacts with dopamine to spark visualiza- tions that cue cravings. Amygdala Neurons here are stimulated by learned emotional responses, such as memories of cravings and pleasure. Ventral pallidum Animal experiments show that damaging this hot spot can turn something that once gave plea- sure into a source of disgust. Brain stem Basic visceral sensations and reactions to pleasure, such as smiling, originate from this hot spot. HIJACKING THE BRAIN New research suggests that the brain’s reward system has different mechanisms for craving and pleasure. Craving is driven by the neurotransmitter dopamine. Pleasure is stimulated by other neurotransmitters in “hedonic hot spots.” When the craving circuitry overwhelms the pleasure hot spots, addiction occurs, leading people to pursue a behavior or drug despite the consequences. PATHWAYS TO CRAVING Desire is triggered when dopamine, which originates near the top of the brain stem, travels through neural pathways to act on the brain. Drugs increase the flow of dopamine. PLEASURE HOT SPOTS A system of small hedonic hot spots, unrelated to dopamine, provides temporary sensations of pleasure and forms a feedback loop with the reward system that controls desire.